In chromatography, a mixture, vaporized in a carrier gas, is introduced into a column where differential migration of the compounds, through the column, results in their separation. The compounds take different times to travel the length of the column. Compounds having more affinity for the packing in the column will tend to be retained in the packing, and their migration through the column will take a longer time. However, as the number of compounds in the mixture increases, it becomes likely that two or more compounds will have similar affinities for the packing and, therefore, their migration times will become close to one another or almost identical. When this occurs, the compounds to not separate, and they will co-elute from the column. One of the ways that can be used to separate the co-eluted chemicals is re-injecting the non-separated compounds into a second chromatographic column as they elute from the first. In this "heart-cutting" technique, the flow of the first column is diverted into a second column temporarily at the elution time of the non-separated components. The chromatographic process continues on the second column which has a different packing, and separation can be achieved, as shown in FIG. 1. In this technique that uses two gas chromatographs combined in series, the mixture has to be re-injected if another "heart-cut" is to be made in order to separate another region of the chromatogram.
A second approach that has been proposed produces multidimensional separation by modulating the temperature of the chromatographic column. In this arrangement, the sample flows through a first column at a given temperature, and the column is continuously modulated in temperature at its end. The temperature is cooled so as to temporarily retain compounds in the flow for a short period of time, and then flash-heated in order to desorb them into a second column in series with the first. Thus, at periodic times, the second column analyzes compounds that have been trapped at the end of the first and acts as a second dimension. The arrangement is shown in FIG. 2. It is limited in the number of compounds that it can ultimately separate because the analysis cycle is short in the second dimension (=2 seconds). Furthermore, the technique has only one mode of operation and cannot be used for the selective and rapid analysis of one or several target compounds present in a mixture. Thus it seems to be better than conventional chromatography and superior to heart-cutting, since it can expand many regions of a chromatogram using a single injection of the sample.
In the field of gas chromatography injectors, it is desirable to inject in the gas phase the substances to be analyzed by the gas chromatograph as a "short square pulse". The start time of passage through the gas chromatographic separation column should be substantially the same for all of the injected sample to be analyzed. When injecting high volumes of sample, conventional injectors have difficulty releasing the substances to be analyzed in an efficient square pulse manner. Furthermore, many complex organic compounds (normally in a solid phase at room temperature) are preferably injected in solution, only for the solvent to be discharged at the temperature of the analysis and for the remaining compounds to be released in gas form at the high temperature of analysis. This known method of injection is limited by the amount of solution which can be injected, due to the possible harmful effect on the gas chromatograph performance caused by a large amount of solvent being discharged in order to release a satisfactory amount of compounds from the solution. Furthermore, the chromatographic column can be saturated or blocked if too high amounts of compound are injected.
It is an object of the present invention to provide an apparatus for superior qualitative analysis of complex chemical mixtures.
It is a further object of the present invention to provide an apparatus and method for the separation and identification of complex chemical mixtures.
In "Zone Gas Chromatography" by Endre Fuggerth, Analytical Chemistry, Vol. 61, No. 14, Jul. 15, 1989, pp. 1478-1485, there is described an apparatus for selectively removing volatile substances. injected into a packing filled column. The disclosed device has a narrow furnace passing over a column in which a substance to be analyzed is injected. As the furnace is passed over the zone containing the packing, substances thermally desorbed are released and carried by a carrier gas passing through the column. When the furnace surpasses the packing zone, the substances released go into a gas chromatography oven. The ability of the disclosed device to efficiently release substances into the gas chromatography (GC) apparatus is limited. Rapid release of the volatile substances from the packing filled column into the GC within a short period of time is lost due to the width of the heated zone or area by the narrow furnace.
It is an object of the present invention to provide an apparatus for superior qualitative analysis of complex chemical mixtures.
It is a further object of the present invention to provide an apparatus and method for the separation and identification of complex chemical mixtures.
It is yet another object of the present invention to provide an apparatus for selectively removing volatile substances injected into a packing filled column in which a very short portion of the column is raised to a desired high temperature and swept over the packing to release volatile substances.